SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1247 AM CDT Wed Apr 20 2022
Valid 201200Z - 211200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
OKLAHOMA INTO SOUTHEAST KANSAS AND EXTREME SOUTHWEST
MISSOURI/NORTHWEST ARKANSAS...
...SUMMARY...
A few supercells are possible late this afternoon and evening from
southeastern Kansas to central/eastern Oklahoma. A few strong storms
may also impact areas west of the Oregon Cascades, accompanied by at
least some risk for severe weather.
...Eastern OK/Southeast KS Vicinity...
An upper-level shortwave trough over the central/southern Rockies at
the beginning of the period will shift east across the Plains during
the afternoon and early evening. Deep-layer flow is not forecast to
be overly strong, with around 30-40 kt expected from around 850-500
mb. However, vertically veering profiles will support effective
shear magnitudes around 40-45 kt. At the surface, low pressure over
central KS will weaken through the day, with an elongated area of
low pressure extending from central/eastern KS into western/central
OK by late afternoon. A dryline is forecast to develop eastward
across central OK/KS, becoming positioned from southeast KS to just
west of the Tulsa vicinity into south-central OK and then
southwestward into central TX. Southerly low-level flow will
transport low to mid 60s dewpoints northward across eastern OK and
southeast KS by peak heating. As midlevel lapse rates steepen with
the approach of the upper trough, this will aid in moderate to
strong destabilization by late afternoon. This large-scale pattern
will generally support a few supercell storms from late afternoon
into the evening.
However, the forecast remains uncertain/conditional. The timing of
the shortwave trough may be sub-optimal for convection. If it ejects
east faster than anticipated, subsidence could limit convective
initiation across much of the Slight risk area. Furthermore,
forecast guidance has become clustered into two camps:
1. convection developing over far northeast OK/southeast KS into
southwest MO.
2. convection developing from central to northeast OK and spreading
southeast into southeast OK.
Most guidance is consistent in maintaining a stronger cap further
north where temperatures will remain somewhat cooler, and northward
transport of better-quality boundary-layer moisture is even more in
question compared to further south. Any convection that does develop
from southeast KS into southwest MO likely will be contending with
stronger inhibition and a narrower moist warm sector, though will
still conditionally support large hail. Most guidance is consistent
in the dryline developing eastward to roughly the I-35 corridor with
a dryline bulge across northeast OK just west of Tulsa. This area
near the I-44 corridor from near/just east of OKC into northeast OK
appears the most likely area for a couple of supercells in the
22-02z time frame. Favorably curved low-level hodographs becoming
elongated above 3 km will support supercells capable of large hail
(some possibly near 2 inches in diameter). Boundary-layer moisture
is still expected to be somewhat shallow, and storms may be
higher-based initially, though some threat will still exist for a
tornado or two given adequate low-level shear and an increasing
southwesterly low-level jet during the evening.
Elevated convection will spread eastward during the late evening
across parts of northern AR and central/southern MO. This activity
will mainly pose a threat for marginally severe hail.
...Western OR...
Southwesterly deep-layer flow will increase as a Pacific upper
trough shifts east toward the Pacific Northwest. Cooling aloft will
result in steep lapse rates and modest destabilization is expected
west of the Cascades. Deep-layer flow will remain mainly
uni-directional, however increasing speed with height will result in
moderate effective shear magnitudes around 25-35 kt. This should
support a few organized cells. Cold temperatures aloft and elongated
hodographs suggest hail will be possible, in addition to locally
strong gusts, with stronger convection. A tornado also will be
possible, though weak instability and modest SRH may temper this
potential.
..Leitman.. 04/20/2022
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